A zoom lens is a lens for changing a focal length by moving a plurality of movable lens groups making up the zoom lens in an optical axis direction. The movable lens groups making up the zoom lens are largely divided into a zoom group comprising one or a plurality of zoom lenses, which mainly functions to change the focal length, and a correction group comprising one or a plurality of lenses, which functions to correct movement of an image plane during a magnification change. Zoom lenses adopting a driving method by which the zoom group moves in one direction during the magnification change, and the correction group moves in one direction and reverses its movement direction to make a U-turn are widely used because of their simple structure and easiness in aberration correction [e.g., JP10-039214A (Patent Document 1), JP11-149044A (Patent Document 2)].
Recently, these zoom lenses have come to be applied also to small-sized cameras such as compact digital cameras. In lens-integrated cameras such as compact digital cameras, there are demands such as reducing a size, and enabling photographing at a position as close as possible to an object. Therefore, a lens is becoming a mainstream, in which instead of mechanically interlocking a correction lens and a variable magnification lens with a cam, a movement locus of a correction lens is stored in a microcomputer in advance as a data table representing a lens cam locus, and the correction lens is driven according to the data table.
In a small size camera or a camera mounted on a mobile device, because of its small lens system, movement of lenses during a magnification change is generally performed by a driving device such as a motor mounted on the camera. Also in the case where each lens is moved using such a driving device, a method in which each lens is moved according to a lens position data table mounted in advance to obtain a desired focal length is commonly applied. On this occasion, lens position data by which all the focal lengths can be sequentially obtained are not written in the lens position data table due to a limitation of data storage capacity, but lens position data corresponding to 5 to 20 discrete focal lengths only are written.
Incidentally, in a conventional zoom lens in which discrete focal lengths are set, and a movement direction of a correction group is reversed, respective focal lengths (zoom magnifications) are set at regular intervals (namely, like f2−f1=f3−f2= . . . , a difference in focal length between two adjacent focal lengths is equal). Therefore, it becomes highly probable that a zoom position (which is a lens position of a respective lens group corresponding to a discretely set focal length) is set at a lens position at which the correction group reverses its movement direction.
If the zoom position has been set at the lens position at which the movement direction is reversed, the zoom position set to the lens position at which the movement direction is reversed is to limit a movement range of the correction group. Therefore, in optical design, it is necessary to perform designing such that a space is secured to prevent interference between lenses from occurring at the zoom position corresponding to the lens position at which the movement direction of the correction group is reversed. In addition, in design for lens holders or a driving portion, because a full stroke of a driving system is determined at the zoom position corresponding to the lens position at which the movement direction is reversed, it is necessary to perform designing such that interference between the lens holders does not occur at the zoom position corresponding to the lens position.
As described above, because the zoom position set at the lens position at which the correction group reverses the movement direction limits the movement range of the correction group, even if attempting to make the zoom lens compact, the zoom lens cannot easily be made compact.
If the full stroke of the correction group can be shortened without changing the optical design, enough space will be provided by reducing a size of a lens driving portion, thus enabling miniaturization of the whole zoom lens. In addition, shortening the full stroke of the correction group would make it possible to achieve a more compact optical design.